In production of semiconductors, liquid crystals, and the like, there is an operation step in which a thin film is formed on a surface of a substrate (a subject to be processed) such as a wafer or a glass plate, or the surface is cleaned or dried. In the operation step, there is used an apparatus that rotates a substrate mounted on a rotary head at a high speed.
For example, in a thin film forming step, an apparatus called a spin coater is used, which rotates at a high speed a substrate having a coating solution dropped thereon, so as to spread the coating solution by centrifugal force, thereby forming a thin film.
As shown in FIG. 9, a structure of a conventional spin coater mainly includes: a discoidal spin head 50 (a rotary head) placed horizontally; a rotating shaft 52 extending downward from the center of a lower surface of the spin head 50; and a driving motor 51 connected to the spin head 50 through the rotating shaft 52. A wafer 53 is mounted on an upper surface of the spin head 50, while a splash-preventing cup 56 is disposed around the wafer 53 so as to cover the entire spin head 50. An upper surface of the splash-preventing cup 56 is open, while a discharge nozzle 55 is placed above the splash-preventing cup 56 in order to supply a coating solution 54 (a processing solution) in a droplet form.
First, the wafer 53 conveyed from a previous step is automatically conveyed and mounted on the spin head 50 by a suction conveyor or the like, and then the wafer 53 is rotated at a high rotation speed (e.g., 4000 rpm, or the like) together with the spin head 50 by using the driving motor 51 through the rotating shaft 52. Next, when the coating solution 54 is dropped onto a surface of the rotating wafer 53 from the nozzle 55, the coating solution 54 spreads on the surface of wafer 53 by centrifugal force to form a thin film. It should be noted that, the excessive coating solution 54 not having contributed to the formation of the thin film is collected by the splash-preventing cup 55 and recovered from the lower part.
A thin film forming step by such a spin coater is performed in an airtight container 58 in a clean environment in order to prevent impurities from mixing into a thin film. Hence, with the rotating shaft 52 being set as a border, a spin coater is usually configured such that the upper part including the spin head 50 is arranged in the airtight container 58, and that the lower part including the driving motor 51 is arranged outside the container 58. With this configuration, since the rotating shaft 52 penetrates though a floor wall 58a of the airtight container 58 in a conventional spin coater, a part penetrated by the rotating shaft 52 is provided with a seal material 57 for maintaining a clean environment in the airtight container.